Knee-joint prosthesis

ABSTRACT

The invention relates to a (knee) joint for positioning two pivoting parts in such a way that they can pivot within a limited range. According to the invention, a combined turning and sliding movement is produced by means of curved guides ( 6, 6′, 7, 7 ′). A cam body ( 8 ) connected to one pivoting part, e.g. the lower leg, has two cams ( 10, 11; 13, 14 ), preferably on each side. Said cams interact with the curved guides ( 6, 6′, 7, 7 ′). The curved guides ( 6, 6′, 7, 7 ′) are located in half-shells ( 3, 4 ) which are connected to the second pivoting part, e.g. the upper leg. Parts of the inventive knee joint which are subject to wear are relatively easy to replace and movement sequences can also be modified when replacements are made.

This application is the US national phase of PCT applicationPCT/AT98/00315 filed Dec. 18, 1998 with a claim to the priority ofAustrian application A2150/97 filed Dec. 19, 1997.

FIELD OF THE INVENTION

The invention relates to a joint (knee joint) for limited relativepivoting of two parts, in particular human body parts, where arcuateguides produce a combined pivoting and sliding.

BACKGROUND OF THE INVENTION

The problem in making various joints, in particular knee joints, ismainly in reproducing the natural movement of the joint, which naturalmovement is not a simple pivoting but a combined pivoting and sliding.

Austrian 393,620 describes a joint for a knee brace where two arcuateguides formed in a first brace part are engaged by two pins limiting thepivot angle of the two brace parts. The pins or bolts thus form in everyposition the axis for the arcuate guiding of the other pins. The naturalmovement of the knee cannot be duplicated by such an arrangement.

U.S. Pat. No. 5,009,223 describes joints for knee braces where inaddition to the two arcuate guides there are two further arcuate guides.These two additional guides form a sort of T, with one T-arm carrying abolt and the other T-arm another bolt of another side rail. Even in thisknown arrangement it is not possible to guide in a natural movement.

OBJECT OF THE INVENTION

The object of the invention is to produce a joint of the above-mentionedtypes that produces a combined pivoting and sliding movement and that isusable in particular but not exclusively as a replacement for a humanknee joint. It should also be possible to relatively easily replacewear-prone parts and even produce by changing parts a different movementpattern.

SUMMARY OF THE INVENTION

This is attained in that a cam body on one of the pivotal parts, e.g.the tibia, preferably has two sides each with two cams that coact withrespective arcuate guides that are formed in cups that are connectedwith the second pivotal part, e.g. the femur.

Such an arrangement produces a combined pivotal and slide movement thatbe adjusted by changing the shape of the arcuate guides for differentrequirements. Replacement of the wear parts is also relatively simple.

According to a preferred embodiment of the invention, the cam body hastwo cylindrical surfaces forming a cam and meeting at a rounded edge andtwo projections extending perpendicular to the pivot direction andforming second cams and the guides are offset in two steps in the cups.With this it is preferable when the cam body is shaped in section as atriangle with rounded corners.

The projecting second cams are formed on the side of the roundedtriangle opposite the point of the two cylindrical surfaces. Theconnection of one of the pivotal parts is arranged opposite the point ofthe two cylindrical surfaces.

In order to hold the two cups these are partially surrounded by a holderon which the connection for the other pivotal part is arranged. The cupsare fitted to the holder so that they can be switched easily.

BRIEF DESCRIPTION OF THE DRAWING

In the following the invention is more closely described with referenceto an embodiment shown in the drawings, without being limited to thisembodiment. Therein:

FIG. 1 is a perspective view of a joint according to the invention;

FIG. 2 is an exploded view of the joint of FIG. 1;

FIG. 3 is a longitudinal section through the joint in an extendedposition;

FIG. 3A illustrates the main guide parts of the joint in the position ofFIG. 3;

FIG. 4 is a longitudinal section through the joint in a maximally flexedposition;

FIG. 4A illustrates the main guide parts of the joint in the position ofFIG. 4; and

FIG. 5 is a section through the joint along a section planeperpendicular to the plane of the view of FIG. 3.

SPECIFIC DESCRIPTION

The embodiment according to the drawing is a knee prosthesis. Therein aholder 1 carries a connection pin 2 that is connected with the femur.The holder 1 is fitted with two cups 3 and 4 that are secured on theholder 1 via bores 5 formed partly in the cups 3 and 4 and partly in theholder 1 and by unillustrated screws. The cups 3 and 4 form arcuateouter guides 6 and 6′ and arcuate center or inner guides 7 and 7′, theguides 7 and 7′ being offset in steps from the respective guides 6 and6′ along an axis perpendicular to the view plane of FIGS. 3 and 4.

The cups 3 and 4 hold a cam body 8 on which a pin 9 is provided that isfitted into the tibia. The cam body 8 is of generally rounded triangularsection. Two cylinder surfaces 10 and 11 meet at a rounded edge 12 thatis opposite the pin 9. These two cylindrical surfaces 10 and 11 form acenter cam of the cam body 8, riding on the arcuate inner or centerguides 7 and 7′.

Outer cams 13 and 14 that coact with the arcuate outer guides 6 and 6′project axially from the sides of the cam body 8. These cams 13 and 14have in the illustrated embodiment an elliptical section, with one part15 of larger radius of curvature also forming the third side of the body8 and the two parts 16 of smaller radius of curvature riding on thearcuate guides 6 and 6′.

As visible in FIGS. 3 and 3A, in an extended position of the joint thecylindrical surface 10 engages the guides 7 and 7′ and the cylindricalsurface 11 engages nothing. In the extended the pin 9 engages the cups 3and 4. In order to ensure exact positioning, mechanical abutment of thepin 9 on the cups 3 and 4 is about 1° ahead of mechanical abutment ofthe cylindrical surface 10 on the guide 7, 7′.

In the most flexed position according to FIGS. 4 and 4A, the pin 9engages the opposite outer edges of the cups 3 and 4. In this positionthe cylindrical surface 10 is out of contact with the guide 7, 7′ andthe cylindrical surface 11 is riding on the guide 7, 7′. Even here it ispreferable when mechanical abutment between the pin 9 and the cups 3 and4 is about 1° ahead of mechanical abutment between the cylindricalsurface 11 and the guide 7.

Numerous variations are possible within the scope of the invention. Thusa joint according to the invention can as a result of the free formationof the control surfaces also be used for other body joints andprosthesis. If a combined pivoting and sliding movement is required inother fields, the joint according to the invention can be used.

What is claimed is:
 1. A prosthetic knee joint for installation betweena pair of leg bones, the joint comprising: a cam body for mounting onone of the bones and having a center cam having a pair ofpart-cylindrical surfaces meeting at a rounded corner, the cam bodybeing formed with a pair of oppositely directed projections having outersurfaces each at least partially offset from the respectivepart-cylindrical surface and forming outer cams flanking and radiallyoffset from the center cam; and a pair of guide cups for mounting on theother of the bones, receiving the cam body, and each formed internallywith respective center and outer arcuate guides engageable in angularlydifferently offset positions of the bones with the respective cams, thecams and guides being shaped such that on pivoting of the cam body inthe guide cups the cams slide on the respective guides.
 2. Theprosthetic knee joint defined in claim 1 wherein the cam body is ofgenerally triangular section at the center cam.
 3. The prosthetic kneejoint defined in claim 1 wherein the projections are offset on the cambody away from the rounded corner.
 4. The prosthetic knee joint definedin claim 1 wherein the cam body has a pin for connection to the onebone, the projections being offset oppositely on the cam body from thepin.
 5. The prosthetic knee joint defined in claim 1, further comprisinga holder provided with a pin for connection to the other bone, the guidecups being mounted on the holder.
 6. The prosthetic knee joint definedin claim 5 wherein the guide cups are separable from the holder.